It is well known in the art that after ordinary mold casting, in the upper partial central position of the casted ingot, there exists a V-shape region enriching of segregates and inclusions. The segregates and inclusions in this area are hard to be removed because of being located in the upper central portion, which will affect the quality of the metal generated and is detrimental to metal containing few segregations and inclusions when being rolled out. What's more, the metal bound with the segregates and inclusions cannot be easily separated from impurities, thereby affecting the improvement of the metal yield.
Currently, most of metal ingots in the world are still casted in this way, and thus a lot of metal cannot be achieved with a high quality and cannot be used effectively and fully, which cause much energy wasting.
In order to achieve clean metal, a secondary melting refining procedure, such as electroslag remelting is needed. This causes a great wasting of manpower and resource. Additionally, a great pressure is also imposed on the environment.
This does not meet the development requirements of energy saving and environmental protection, which is the great loss of the metal smelting industry.
In addition, electroslag remelting secondary melting refining procedure requires a great deal of electrical energy, meanwhile, low efficiency also restricts the large scale industrial production. What's worse, the slag material contains large amount of calcium fluoride which will pollute environment, so a de-dust and de-fluorine device must be provided. And the electric arc could seriously damage the crystallizer. A crystallizer casting mold in the manner of electroslag furnace remelting can only refine scores of furnace of steel, which increases the cost of production.
Recently, there exists a clean metal ingot mold. The process for cooling of the bottom mold plate is accelerated in the form of water-cooling. All of the peripheral mold plate or part thereof is water-cooled. The heat preservation dead head portion and the heat preservation portion of the peripheral mold plate keeps at a high temperature to ensure its directional solidification. During the process of directional solidification, the directional crystallization start from the water-cooled mold plate to the high temperature mold plate. The inclusions and segregates were driven to the direction of uncrystallized region in the process of forming crystals. The liquid metal near the high temperature mold plate becomes solidification at last because of being far away from low-temperature. Most of the inclusions and segregates in the liquid metal are enriched in the region that contacts the high temperature mold plate, so the alloy segregations and inclusions can be easily removed with flame or other processing methods, thus achieving the purpose of transferring, removing segregations and inclusions from the liquid metal and getting purified ingot.
However, since the directional solidification is very susceptive to the surroundings, if the portion that does not need to be solidified is exposed to low temperature, it will inevitably solidify preferentially. This will affect not only the movement direction of the alloy segregations, inclusions, but also the comprehensive generation of columnar crystals in the process of directional solidification, which is not favoring to improve the crystal quality and product quality.